Physical Danger
Sunburn, athlete's foot, calluses...there's a long list of mild, sports-related injuries, and they're all possibilities as a caddie. Yes, you do all of the dirty work, from foraging for lost balls in the woods to risking sore limbs as a result of bad posture. But, even with all those possible problems, you're generally not in much danger.
There are some super-unlikely accidents that could happen, such as being struck by a loose golf ball or club, not to mention the odd golf cart accident. But if you drink plenty of water, get yourself some padded shoe soles, and keep your head up, you'll be okay.